Activity of Fly Ash-Derived ZSM-5 and Zeolite X on Fast Pyrolysis of Millettia (Pongamia) Pinnata Waste

Abstract

Fly ash (FA), a by-product of coal combustion, is considered as waste due to its high content of lime and other impurities and is either disposed of in landfills or recycled. Utilization of waste FA as a starting material for the synthesis of zeolite catalysts is a promising solution to reuse this waste. Meanwhile, de-oiled Millettia (Pongamia) pinnata seed waste (PPW) is produced in large amounts from the bio-oil extraction process. This waste is of no value due to its toxicity. However, it was previously shown that the fast pyrolysis of PPW to produce biofuels resulted in oleic acid and other oxygenated (O)-compounds as the main composition (67.2%) with smaller levels of hydrocarbons (HCs). In this work, the catalytic upgrading fast pyrolysis of PPW over the FA-derived ZSM-5 (FA-ZSM-5) and zeolite X (FA-X) catalysts to enhance the formation of HCs was performed using a pyrolyzer interfaced with gas chromatography-mass spectrometry (Py-GCMS), using various biomass to catalyst (B:C) weight ratios (1:1, 1:5 and 1:10). The FA-ZSM-5 and FA-X were derived from FA by alkali hydrothermal and alkali fusion methods, respectively. The result demonstrated that the pyrolysis vapors of PPW had a high content of undesirable components, such as carboxylic acids, oleic acid and other O-compounds (67.2%), whereas the aliphatic and aromatic HC contents were markedly lower. The presence of the synthesized FA-ZSM-5 or FA-X catalysts resulted in a major improvement in the pyrolysis vapor quality. Selectivity on total HCs (aliphatic and aromatic) was significantly increased with greater catalyst contents for both FA-ZSM-5 (90.6%) and FA-X (84.9%). FA-ZSM-5 exhibited a high selectivity for aromatic HCs (82.6%) while zeolite-X showed a higher selectivity towards aliphatic HCs (71.0%). The level of O-compounds was substantially decreased to 1.12% and 21.9% with FA-ZSM-5 at a B:C ratio of 1:10 and FA-X at a B:C ratio of 1:5, respectively. In addition, FA-ZSM-5 and FA-X reduced the content of nitrogenated-compounds from 24.8% (no catalyst) to 8.3% and 0.0%, respectively. Overall, the results suggest that FA-ZSM-5 had a higher HC selectivity and was more effective in promoting deoxygenation reactions, whereas FA-X significantly enhanced the denitrogenation reaction.